(a) Field of the invention
The present invention relates to a microscope, and more specifically a coarse/fine adjustment coaxial handle for feeding a microscope stage.
(b) Description of the prior art
Most of the conventional stage feeding mechanisms for microscopes have only the fine adjustment handle, and a few have both the fine adjustment handle and the coarse adjustment handle. The stage feeding mechanisms having both the handles are so designed as to perform switching between the coarse adjustment and fine adjustment by switching a half nut between fixed condition and non-fixed condition, thereby posing a problem that the tedious procedures are required. Further, the coarse/fine adjustment coaxial handle for driving the microscope tube is equipped with a small-diameter fine adjustment handle located within the coarse adjustment handle and feeds the stage for a relatively long distance at a predetermined rotational angle, thereby incapable of feeding stage for a very short distance. Furthermore, since the coarse adjustment usually causes stage feeding for rather a long distance, it is necessary to re-grip the coarse adjustment handle repeatedly, thereby posing a problem that the onerous and time-consuming operations are required. Moreover, certain stage feeding mechanisms equipped with both the coarse adjustment handle and the fine adjustment handle are of the type wherein the feed screw shaft is rotated integrally with the gear supporting member, i.e., in the directly coupled condition without functioning the reduction gear mechanism when the coarse adjustment handle is turned, and the feed screw mechanism is rotated while functioning the reduction gear mechanism with the gear supporting membe fixed, i.e., in the speed reduction condition. In case of the stage feeding mechanism of this type, however, the coarse adjustment is impossible when the gear supporting member is fixed completely and, in addition, torque cannot be released during the fine adjustment when the rotation of the feed screw shaft is stopped by an external force (when the stage is stopped by a stopper), thereby imposing overload on the engaged portions, etc. of the gears. In order to avoid this overload, it was conventionally practised to impart frictional resistance to the gear supporting member by using an elastic pressing member so that the gear supporting member is moved integrally with the reduction gear (not rotated) during the coarse adjustment against said frictional resistance, whereas the reduction gear is rotated with the gear supporting member fixed by said frictional resistance during the fine adjustment, and when the rotation of the feed screw shaft is stopped by the external force, the gear supporting member is rotated against said frictional resistance during both the coarse and fine adjustments, whereas the opposite handles, i.e., the fine adjustment handle and the coarse adjustment handle are idled by way of the reduction gear. In this case, however, there has been posed a problem that coarse adjustment cannot be performed easily due to too large torque to be required when the frictional resistance is too high though fine adjustment is performed securely when the frictional resistance is adequate.